This invention relates to print hammer assemblies and, more particularly, to print hammer assemblies used in impact serial printers of the type including a platen, a plurality of print elements and a marking medium interposed between the print elements and the platen. An example of an impact serial printer of this type is disclosed in U.S. Pat. No. 4,091,911, whereas an example of a print hammer assembly used in such a printer is disclosed in U.S. Pat. No. 4,037,532.
One problem with existing serial printers of the type disclosed in U.S. Pat. No. 4,091,911, which employ a rotatable print wheel mounted to a linearly movable carriage along with a print hammer assembly, the carriage being moved along a path parallel to the longitudinal axis of an adjacent cylindrical platen, has to do with misalignment of the platen. More specifically, the platen must be precisely aligned relative to the carriage such that the carriage path is parallel to the longitudinal axis of the platen. If this relationship is not true, the print elements of the wheel may impact the platen at other locations on the periphery, but not in alignment with the center line thereof during linear advancement of the carriage. For example, if the platen is inclined in a vertical plane from left to right, the top area of print elements impacting the left portion of the platen might be at least partially deleted, with the reverse being true with respect to impacts occurring at the right portion of the platen. This, of course, will lead to an uneven and perhaps unintelligible print.
U.S. Application Ser. No. 91605 filed concurrently herewith in the names of Richard G. Crystal et al for PRINT HAMMER ASSEMBLY WITH MULTI-LOCATION IMPACTS and assigned to the assignee of the present invention is directed to a print hammer assembly that compensates for minor misalignments of the platen axis relative to the linear path of movement of the carriage to which the print hammer assembly and print elements are mounted. Specifically, this is accomplished by altering the location of maximum impact force of the hammer element following the initial impact of the hammer element against an adjacent platen or an interposed print element against the platen.
It would be desirable, therefore, to provide a print hammer assembly that would compensate for more pronounced misalignments of the platen axis relative to the linear path of movement of the carriage to which the print hammer assembly and print elements are mounted.
In accordance with the present invention, a print hammer assembly is provided comprising a hammer element; a hammer actuator capable when energized of directing said hammer element under force toward an adjacent platen; and means coupled to said hammer element for altering the location of maximum impact force of said hammer element against said platen or an interposed print element against platen, said means for altering including a plurality of adjacent, non-parallel spring members each coupled at one end to said hammer element. Preferably, a pair of normally planar leaf springs are employed.
By offsetting the pair of leaf springs relative to one another, so that they are non-parallel, the effect of altering the location of maximum impact force following initial impact may be amplified over the effect achieved by using parallel leaf springs. This is accomplished due to the trapezoidal configuration of the offset leaf springs as connected to the hammer element at one end and to a support structure at the other end. The trapezoidal configuration imparts a more pronounced shift in maximum impact force location following initial impact than would a strict parallelogram formed by parallel leaf springs. Consequently, more pronounced misalignments of the platen axis may be compensated for through the use of offset leaf springs in the arrangement above-described.
In accordance with the preferred embodiment, a print hammer assembly is provided comprising a support structure having a plunger at a first location thereon; means for movably mounting said support structure with its plunger adjacent an electromagnetic actuator capable of being selectively energized such that when said actuator is energized the resultant magnetic field acting upon plunger will cause said plunger and thus said support structure to travel along predefined paths at predetermined speeds; a hammer element coupled to said support structure at a second location thereon; and means coupled to said hammer element for causing said hammer element to impact an adjacent platen or print element against said platen more than once during travel of said pole piece along its predefined path, said means for causing including a pair of adjacent, substantially identical normally planar spring members that lie in intersecting planes, said spring members cooperating with said support structure to alter the location of maximum impact force of said hammer element against said platen or said print element against said platen for each succeeding impact following the initial impact during travel of said plunger along its predefined path in response to a single energization of said actuator.
These and other aspects and advantages of the invention will be described in more detail below with reference to the accompanying drawings.